Liquid crystalline biphenyls

ABSTRACT

Liquid crystalline compounds of the formula ##SPC1## 
     Wherein R is as hereinafter set forth, which are useful as dielectrics in electro-optical devices, are described.

BRIEF SUMMARY OF THE INVENTION

The invention relates to compounds of the formula ##SPC2##

Wherein R is straight-chain alkyl of 3 to 8 carbon atoms orstraight-chain alkoxy of 3 to 10 carbon atoms.

The compounds of formula I are useful as dielectrics in electro-opticalapparatuses.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to compounds of the formula ##SPC3##

Wherein R is straight-chain alkyl of 3 to 8 carbon atoms orstraight-chain alkoxy of 3 to 10 carbon atoms.

The compounds of formula I have, in the liquid crystalline state, apositive anisotropy of the dielectric constants, i.e., ε.sub.∥ >ε.sub.|, wherein ε.sub.∥ is the dielectric constant along thelongitudinal axis of the molecule and ε.sub.| is the dielectric constantperpendicular thereto.

In an electric field the nematic liquid crystals of the inventionorientate themselves (because ε.sub.∥ > ε.sub.|) in the direction oftheir largest dielectric constant, that is, with their longitudinalaxis, parallel to the direction of the field. This effect is utilized,inter alia, in the interaction between embedded molecules and the liquidcrystalline molecules (guest-host interaction) described by J. H.Helmeier and L. A. Zanoni [Applied Physics Letters 13, 91 (1968)].Another interesting application of the dielectric field orientation isin the rotation cell discovered by M. Schadt and W. Helfrich [AppliedPhysics Letters 18, 127 (1971)], as well as in the Kerr cell describedin Molecular Crystals and Liquid Crystals 17, 355 (1972).

In the electro-optical rotation cell there is present essentially acondenser with transparent electrodes whose dielectric is formed from anematic substance with ε.sub.∥ > ε.sub.|. The longitudinal axes of themolecules of the liquid crystals are arranged in twisted form betweenthe condenser plates in the fieldless state, the twisted structure beingdetermined by the given wall orientation of the molecules. After theapplication of an electric potential to the condenser plates, themolecules adjust themselves with their longitudinal axes in the fielddirection, i.e., perpendicular to the surface of the plates, by whichmeans linear polarized light is no longer rotated in the dielectric (theliquid crystal is uniaxially perpendicular to the surface of theplates). This effect is reversible and can therefore be used to controlthe optical transmissivity of the condenser.

In such a "light rotation cell" it is desirable to use compounds whichpossess a low melting point, broad nematic range, high stability andslight viscosity. The hitherto used compounds or mixtures with liquidcrystalline properties have the disadvantage that at least one of theserequirements is not always sufficiently satisfied. It has nowsurprisingly been found that the compounds of formula I of the inventionpossess liquid crystalline properties which meet with all of theserequirements. They not only have the necessary strong positiveanisotropy of the dielectric constants, but, especially in the form oftheir mixtures with one another or with other other nematic ornon-nematic substances, they are liquid crystalline at relatively lowtemperature, show a slight viscosity, a wide nematic range and a highstability. The operation of electro-optical devices is accordinglypossible with lower voltage, shorter susceptibility, i.e., responsivetime. Moreover, because of the high stability of the compounds offormula I, they can be handled more readily.

Preferred among the compounds of formula I are those wherein R is alkylof 4 to 6 carbon atoms. Especially preferred is the compound of formulaI wherein R is = n-butyl, i.e., 4'-cyano-4-biphenyl valerate. Alsopreferred are compounds of formula I wherein R is pentyloxy, heptyloxyor octyloxy.

The compounds of formula I can be prepared as follows:

a. to prepare a compound wherein R is alkyl, a compound of the formula

    R'COX                                                      II

wherein R' is straight-chain alkyl with 3 to 8 carbon atoms and X is aleaving group, is reacted with 4'-cyano-4-hydroxy-biphenyl or an alkalior alkaline earth metal salt thereof; or

b. to prepare a compound wherein R is alkoxy, a compound of the formula

    R"COX'                                                     III

wherein R" is straight-chain alkoxy with 3 to 10 carbon atoms and X' ishalogen, is reacted with 4'-cyano-4-hydroxy-biphenyl or an alkali oralkaline earth metal salt thereof.

As used herein, the term "leaving group" denotes halogen; hydroxy; loweralkoxy, preferably methoxy or ethoxy; alkaoyloxy, preferably ##EQU1##aryl lower alkoxy, preferably benzyloxy; lower alkylsulfonyloxy,preferably mesyloxy; and arylsulfonyloxy, preferably tosyloxy. The term"halogen" denotes fluorine, chlorine, bromine and iodine.

In process embodiment (a) of the invention, 4'-cyano-4-hydroxy-biphenylor an alkali or alkaline earth metal salt thereof is acylated in a knownmanner. In principle, there come into consideration all esterifyingreactions which are known in the literature, apart from those which areso reactive that the cyano group is concomitantly affected. Preferred,however, are the processes which do not work with an excess of thealcohol reactant.

Thus, 4'-cyano-4-hydroxy-biphenyl can be reacted with a compound offormula II wherein X is halogen, especially chlorine. The reaction isconveniently carried out in an inert organic solvent such as, forexample, diethyl ether, tetrahydrofuran, dioxane, methylene chloride,chloroform, benzene, toluene, cyclohexane or the like. In order to bindthe hydrogen halide liberated in the reaction, it is convenient to usean acid binding agent. Suitable acid binding agents comprise tertiaryamines, pyridines, quinolines or the like. The acid binding agent ispreferably used in a large excess so that it can simultaneously servenot only as an acid binding agent but also as the solvent. The reactionis carried out at room temperature or lower temperatures, preferably at0°-5°C.

An alkali or alkaline earth metal salt of 4'-cyano-4-hydroxy-biphenyl,preferably a sodium, potassium or calcium salt thereof, can also bereacted with a compound of formula II wherein X is halogen--especiallychlorine. The reaction is conveniently effected in an inert organicsolvent, but it can also be carried out in an aqueous solution.

The compounds of formula II wherein X is chlorine can be obtained, forexample, by reaction of the corresponding acid with phosphorustrichloride, phosphorus oxychloride, phosphorus pentachloride or thionylchloride. The soobtained compound need not be isolated from the reactionmixture prior to the reaction with 4'-cyano-4-hydroxy-biphenyl or analkali or alkaline earth metal salt thereof.

Furthermore, the 4'-cyano-4-hydroxy-biphenyl can be reacted with acompound of formula II wherein X is alkanoyloxy. Advantageously, thereis employed as the compound of formula II the acid anhydride ##EQU2##wherein R' is as previously described. Preferably,4'-cyano-4-hydroxy-biphenyl is warmed with an excess of an acidanhydride under the action of a basic catalyst, for example, sodiumacetate or tertiary organic bases, such as pyridine, triethylamine,dimethylaniline, quinoline, or the like; or an acid catalyst such assulfuric acid or boron trifluoride etherate.

The 4'-cyano-4-hydroxy-biphenyl can also be reacted with a compound offormula II wherein X is alkoxy, especially methoxy or ethoxy. Thisreaction is conveniently effected in the presence of a small percent ofhydrochloric or sulfuric acid and boiling under reflux. This alcoholysiscan, however, also be catalyzed by means of a base, for example, usingsodium acetate.

Additionally, the 4'-cyano-4-hydroxy-biphenyl can be reacted with acompound of formula II wherein X is hydroxy. This esterification can beeffected in the presence of an acid-binding additive such as calciumcarbide, calcium hydride, calcium, magnesium, iron, nickel or coppersulfate, or potassium pyrosulfate. A carbodiimide--preferably in thepresence of pyridine--can also be used as the acid-binding additive.Finally, this esterification can also be effected in the presence ofcatalytic amounts of a proton-donating agent, for example, Lewis acid,such as sulfuric acid, hydrochloric acid, toluenesulfonic acid,chlorosulfonic acid or boron trifluoride.

In process embodiment (b) of the invention, 4'-cyano-4-hydroxy-biphenylis reacted with a compound of formula III wherein X ishalogen--especially chlorine. The reaction is conveniently carried outin an inert organic solvent such as diethyl ether, tetrahydrofuran,dioxane, methylene chloride, chloroform, benzene, toluene, orcyclohexane. In order to bind the hydrogen halide liberated in thereaction, it is convenient to use an acid-binding agent. Suitableacid-binding agents comprise tertiary amines, pyridines, quinolines, andthe like. Preferably, the acid-binding agent is used in large excess sothat it can simultaneously serve not only as the acid-binding agent butalso as the solvent. The reaction is carried out at room temperature orlower temperatures, preferably 0°-5°C.

An alkali or alkaline earth metal salt of 4'-cyano-4-hydroxy-biphenyl,preferably a sodium, potassium or calcium salt thereof, can also bereacted with a compound of formula III wherein X' is halogen--especiallychlorine. The reaction is conveniently effected in an inert organicsolvent, but it can also be carried out in an aqueous solution.

The physical properties of the compounds of formula I of the inventionare illustrated in the following Table I:

                  TABLE I                                                         ______________________________________                                                    Melting Point                                                                              Clearing Point                                       R           (m.p.) °C                                                                           (Cl.p.) °C.                                   ______________________________________                                        n-Propyl    77.9-78.2    74.7      a)                                         n-Butyl     36.5-36.9    61.7                                                 n-Pentyl    56.1         70.7                                                 n-Hexyl     57.7-57.9    68.8                                                 n-Heptyl    77.5-77.9    74.1      a)                                         n-Octyl     43.2-43.6    74.0      b)                                         n-Propyloxy 70.2-70.9    68.2      a)                                         n-Butyloxy  64.8-65.7    64.3      a)                                         n-Pentyloxy 50.1-51.0    61.1                                                 n-Hexyloxy  87.1-87.5    62.7      a)                                         n-Heptyloxy 50.2-50.5    65.2                                                 n-Octyloxy  51.6-52.4    67.7                                                 n-Nonyloxy  53.0-53.1    70.0      c)                                         n-Decyloxy  59.3-60.0    74.0      d)                                         ______________________________________                                        a) monotrope     b) smectic up to 61.3°                                c) smectic up to 68.1°                                                                  d) smectic up to 74.0°                            

The compounds of formula I of the invention can be used in the form oftheir mixtures with one another, mixtures which correspond to a eutecticare especially preferred.

The compounds of formula I of the invention are preferably used in theform of their mixtures with other nematic or non-nematic substances suchas, for example, with Schiff's bases of the formula ##SPC4##

wherein R₁ is straight-chain alkyl of 2 to 8 carbon atoms,straight-chain alkoxy of 4 to 7 carbon atoms, straight-chain alkanoyloxyof 2 to 8 carbon atoms or straight-chain alkylcarbonate of 2 to 11carbon atoms.

Furthermore, the compounds of formula I of the invention can also beused in the form of their mixtures with compounds of the formula##SPC5##

wherein R₂ is straight-chain alkyl of 4 to 7 carbon atoms orstraight-chain alkylcarbonate of 2 to 11 carbon atoms, or with compoundsof the formula ##SPC6##

wherein R₃ is straight-chain alkyl of 4 to 8 carbon atoms,straight-chain alkoxy with 5 to 8 carbon atoms or straight-chainalkylcarbonate with 3 to 11 carbon atoms, or with compounds of theformula ##SPC7##

wherein R₄ is straight-chain alkyl such as, for example, n-pentyl,n-hexyl or n-heptyl or straight-chain alkoxy, such as, for example,n-pentyloxy, n-hexyloxy or n-heptyloxy.

The compounds of formula IV wherein R₁ is straight-chain alkylcarbonateare novel and can be manufactured by condensation of a compound of theformula ##SPC8##

wherein R₁ ' is a straight-chain alkylcarbonate of 2 to 11 carbon atoms,with p-aminobenzonitrile.

The compounds of formula V wherein R₂ is straight-chain alkylcarbonateare likewise novel and can be prepared by condensation of ##SPC9##

wherein R₂ ' is a straight-chain alkylcarbonate of 2 to 11 carbon atoms,with p-cyanobenzaldehyde.

The compounds of formula VI wherein R₃ is straight-chain alkylcarbonateare likewise novel and can be prepared by reaction of a compound of theformula ##SPC10##

wherein R₃ ' is a straight-chain alkylcarbonate of 3 to 11 carbon atoms,with p-hydroxybenzonitrile.

Especially preferred are the following mixtures:

33.3 Mol-% 4'-cyano-4-biphenylyl pentyl carbonate with

33.3 Mol-% 4'-cyano-4-biphenylyl heptyl carbonate and

33.3 Mol-% 4'-n-hexyl-4-cyanobiphenyl, m.p. 6.6°C., cl.p. 51°C;

50 Mol-% 4'-cyano-4-biphenylyl heptyl carbonate and

50 Mol.-% p-n-heptylbenzoic acid p' -cyanophenyl ester, m.p. -2°C, cl.p.58°C;

33.3 Mol-% 4'-cyano-4-biphenylyl pentyl carbonate with

33.3 Mol-% 4'-cyano-4-biphenylyl octyl carbonate and

33.3 Mol-% 4'-n-hexyl-4-cyanobiphenyl, m.p. < -20°C, cl.p. 51°C;

33.3 Mol-% 4'-cyano-4-biphenylyl octyl carbonate with

33.3 Mol-% 4'-cyano-4-biphenylyl pentyl carbonate and

33.3 Mol-% 4'-n-heptyl-4-cyanobiphenyl, m.p. < -20°C, cl.p. 55°C;

33.3 Mol-% 4'-cyano-4-biphenylyl octyl carbonate with

33.3 Mol-% 4'-cyano-4-biphenylyl hexanoate and

33.3 Mol-% 4'-n-heptyl-4-cyanobiphenyl, m.p. < -20°C, cl.p. 58°C;

33.3 Mol-% 4'-cyano-4-biphenylyl octyl carbonate with

33.3 Mol-% p-(p-cyanophenoxy)carbonyl phenyl n-heptyl carbonate and

33.3 Mol-% 4'-n-heptyl-4-cyanobiphenyl, m.p. 17°C, cl.p. 59°C;

33.3 Mol-% 4'-cyano-4-biphenylyl octyl carbonate with

33.3 Mol-% 4'-cyano-4-biphenylyl hexanoate and

33.3 Mol-% p-(p-hexylbenzyliden)amino benzonitrile, m.p. < -20°C, cl.p.66.5°C;

33.3 Mol-% 4'-cyano-4-biphenylyl octyl carbonate with

33.3 Mol-% 4'-cyano-4-biphenylyl pentyl carbonate and

33.3 Mol-% p-(p-n-hexylbenzyliden)amino benzonitrile, m.p. < -20°C,cl.p. 66°C;

33.3 Mol-% 4'-cyano-4-biphenylyl octyl carbonate with

33.3 Mol-% 4'-cyano-4-biphenylyl valerate and

33.3 Mol-% p-(p-propylbenzyliden)amino benzonitrile, m.p. < -20°C, cl.p.65°C.

The preparation of the compounds of formula I as well as the compoundsof formulas IV, V and VI wherein R₁, R₂ or R₃ is straight-chainalkylcarbonate is illustrated by the following Examples. Alltemperatures are given in degrees Centigrade, unless otherwisespecified.

EXAMPLE 1 Preparation of 4'-cyano-4-biphenylyl butyrate

0.390 G. of 4'-cyano-4-hydroxy-biphenyl are dissolved in 4.0 ml. ofabsolute pyridine and cooled to -10° with stirring. 0.255 G. of butyricacid chloride are added dropwise thereto over a period of 2 minutes. Thetemperature rises to 0° and pyridine hydrochloride precipitates out.Subsequently, the mixture is stirred overnight at room temperature andthe suspension poured on to a mixture of 12 g. of ice and 12 ml. of 20%hydrochloric acid. Thereafter, this mixture is extracted three timeswith ethyl acetate, washed with water, dried over sodium sulfate andevaporated in vacuum. The 0.552 g. of yellowish crystals obtained as theresidue are dissolved in benzene and chromatographed on 40 g. of silicagel. Benzene elutes 0.521 g. of yellowish crystals which arerecrystallized from acetone-hexane up to constant melting point andclearing point. The pure 4'-cyano-4-biphenylyl butyrate obtained meltsat 77.9°-78.2° and is liquid crystalline (monotrope) upon cooling to74.7°. UV (EtOH): ε₂₇₂ = 26,100.

EXAMPLE 2 Preparation of 4'-cyano-4-biphenylyl valerate

0.390 G. of 4'-cyano-4-hydroxy-biphenyl are dissolved in 4.0 ml. ofabsolute pyridine and reacted with 0.289 g. of valeric acid chloride asin Example 1. The 0.590 g. of brownish colored turbid oil obtainedaccording to the procedure described in Example 1 are dissolved inbenzene and chromatographed on 40 g. of silica gel. Benzene elutes 0.518g. of a colorless, turbid oil which crystallizes upon trituration. It isrecrystallized from acetone-hexane up to constant melting point andclearing point. The pure 4'-cyano-4-biphenylyl valerate obtained meltsat 36.5°-36.9° and has a clearing point of 61.7°. UV (EtOH): ε₂₇₁ =25,800.

EXAMPLE 3 Preparation of 4'-cyano-4-biphenylyl hexanoate

0.390 G. of 4'-cyano-4-hydroxy-biphenyl are dissolved in 4.0 ml. ofabsolute pyridine and reacted with 0.323 g. of caproic acid chloride asin Example 1. The 0.613 g. of yellowish crystals obtained according tothe procedure described in Example 1 are dissolved in benzene andchromatographed on 40 g. of silica gel. Benzene elutes 0.555 g. ofcolorless crystals which are recrystallized from acetone-hexane up toconstant melting point and clearing point. The pure4'-cyano-4-biphenylyl hexanoate obtained melts at 56.1° and has aclearing point of 70.7°. UV (EtOH): ε₂₇₃ = 26,400.

EXAMPLE 4 Preparation of 4'-cyano-4-biphenylyl heptanoate

0.390 G. of 4'-cyano-4-hydroxy-biphenyl are dissolved in 4.0 ml. ofabsolute pyridine and reacted with 0.356 g. of oenanthic acid chlorideas in Example 1. The 0.671 g. of yellow crystals obtained according tothe procedure described in Example 1 are dissolved in benzene andchromatographed on 40 g. of silica gel. Benzene elutes 0.581 g. ofcolorless crystals which are recrystallized from acetone-hexane up toconstant melting point and clearing point. The pure4'-cyano-4-biphenylyl heptanoate obtained melts at 57.7°-57.9° and has aclearing point of 68.8°. UV (EtOH): ε₂₇₂ = 26,800.

EXAMPLE 5 Preparation of 4'-cyano-4-biphenylyl octanoate

0.390 G. of 4'-cyano-4-hydroxy-biphenyl are dissolved in 4.0 ml. ofabsolute pyridine and reacted with 0.390 g. of caprylic acid chloride asin Example 1. The 0.671 g. of yellowish crystals obtained according tothe procedure described in Example 1 are dissolved in benzene andchromatographed on 40 g. of silica gel. Benzene elutes 0.586 g. ofcolorless crystals which are recrystallized from acetone-hexane up toconstant melting point and clearing point. The pure4'-cyano-4-biphenylyl octanoate obtained melts at 77.5°-77.9° and isliquid crystalline (monotrope) upon cooling to 74.1°. UV (EtOH): ε₂₇₂ =26,500.

EXAMPLE 6 Preparation of 4'-cyano-4-biphenylyl nonanoate

0.390 G. of 4'-cyano-4-hydroxy-biphenyl are dissolved in 4.0 ml. ofabsolute pyridine and reacted with 0.424 g. of pelargonic acid chlorideas in Example 1. The 0.722 g. of yellow crystals obtained according tothe procedure described in Example 1 are dissolved in benzene andchromatographed on 40 g. of silica gel. Benzene elutes 0.617 g. ofcolorless crystals which are recrystallized from acetone-hexane up toconstant melting point and clearing point. The pure4'-cyano-4-biphenylyl nonanoate obtained melts at 43.2°-43.6° and has aclearing point of 74.0°. The compound is smectic up to 61.3°. UV (EtOH):ε₂₇₂ = 26,900.

EXAMPLE 7 Preparation of 4'-cyano-4-biphenylyl n-propyl carbonate

0.390 G. of 4'-cyano-4-hydroxy-biphenyl are dissolved in 4.0 ml. ofabsolute pyridine and reacted with 0.293 g. of chloroformic acidn-propyl ester as in Example 1. The 0.546 g. of brownish crystalsobtained according to the procedure described in Example 1 are dissolvedin benzene and chromatographed on 40 g. of silica gel. Benzene elutes0.528 g. of yellowish crystals which are recrystallized fromether-hexane up to constant melting point and clearing point. The pure4'-cyano-4-biphenylyl n-propyl carbonate obtained melts at 70.2°-70.9°and is liquid crystalline (monotrope) upon cooling to 68.2°. UV (EtOH):ε₂₇₀ = 26,000.

EXAMPLE 8 Preparation of 4'-cyano-4-biphenylyl n-butyl carbonate

0.390 G. of 4'-cyano-4-hydroxy-biphenyl are dissolved in 4.0 ml. ofabsolute pyridine and reacted 0.328 g. of chloroformic acid n-butylester as in Example 1. The 0.579 g. of colorless oil obtained accordingto the procedure described in Example 1 crystallizes after trituration.The crystals are dissolved in benzene and chromatographed on 40 g. ofsilica gel. Benzene elutes 0.521 g. of colorless crystals which arerecrystallized from ether/hexane up to constant melting point andclearing point. The pure 4'-cyano-4-biphenylyl n-butyl carbonateobtained melts at 64.8°-65.7° and is liquid crystalline (monotrope) uponcooling to 64.3°. UV (EtOH): ε₂₇₀ = 26,300.

EXAMPLE 9 Preparation of 4'-cyano-4-biphenylyl n-pentyl carbonate

0.976 G. of 4'-cyano-4-hydroxy-biphenyl are dissolved in 10 ml. ofabsolute pyridine and reacted with 0.90 g. of chloroformic acid n-pentylester as in Example 1. The 1.5 g. of yellow, partially crystallized oilobtained according to the procedure described in Example 1 is dissolvedin benzene and chromatographed on 90 g. of silica gel. Benzene elutes1.479 g. of colorless crystals which are recrystallized fromether-hexane up to constant melting point and clearing point. The pure4'-cyano-4-biphenylyl n-pentyl carbonate obtained melts at 50.1°-51.0°and has a clearing point of 61.1°. UV (EtOH): ε₂₇₀ = 26,800.

EXAMPLE 10 Preparation of 4'-cyano-4-biphenylyl n-hexyl carbonate

0.976 G. of 4'-cyano-4-hydroxy-biphenyl are dissolved in 10 ml. ofabsolute pyridine and reacted with 0.988 g. of chloroformic acid n-hexylester as in Example 1. The 1.675 g. of yellowish, turbid, partiallycrystallized oil obtained according to the procedure described inExample 1 is dissolved in benzene and chromatographed on 80 g. of silicagel. Benzene elutes 1.530 g. of colorless crystals which arerecrystallized from ether-hexane up to constant melting point andclearing point. The pure 4'-cyano-4-biphenylyl n-hexyl carbonateobtained melts at 87.1°-87.5° and is liquid crystalline (monotrope) uponcooling to 62.7°. UV (EtOH): ε₂₇₀ = 26,300.

EXAMPLE 11 Preparation of 4'-cyano-4-biphenylyl n-heptyl carbonate

0.976 G. of 4'-cyano-4-hydroxy-biphenyl are dissolved in 10 ml. ofabsolute pyridine and reacted with 1.07 g. of chloroformic acid n-heptylester as in Example 1. The 1.8 g. of yellow oil obtained according tothe procedure described in Example 1 is dissolved in benzene andchromatographed on 90 g. of silica gel. Benzene elutes 1.782 g. ofcolorless crystals which are recrystallized from ether-hexane up toconstant melting point and clearing point. The pure4'-cyano-4-biphenylyl n-heptyl carbonate obtained melts at 50.2°-50.5°and has a clearing point of 65.2°. UV (EtOH): ε₂₇₀ = 25,900.

EXAMPLE 12 Preparation of 4'-cyano-4-biphenylyl n-octyl carbonate

0.390 G. of 4'-cyano-4-hydroxy-biphenyl are dissolved in 10 ml. ofabsolute pyridine and reacted with 0.423 g. of chloroformic acid n-octylester as in Example 1. The 0.721 g. of brownish oil obtained accordingto the procedure described in Example 1 is dissolved in benzene andchromatographed on 40 g. of silica gel. Benzene elutes 0.620 g. ofcolorless crystals which are recrystallized from ether-hexane up toconstant melting point and clearing point. The pure4'-cyano-4-biphenylyl n-octyl carbonate obtained melts at 51.64° and hasa clearing point of 67.7°. UV (EtOH): ε₂₇₀ = 26,000.

EXAMPLE 13 Preparation of 4'-cyano-4-biphenylyl n-nonyl carbonate

0.976 G. of 4'-cyano-4-hydroxy-biphenyl are dissolved in 10 ml. ofabsolute pyridine and reacted with 1.24 g. of chloroformic acid n-nonylester as in Example 1. The 2.026 g. of yellowish, turbid oil obtainedaccording to the procedure described in Example 1 is dissolved inbenzene and chromatographed on 90 g. of silica gel. Benzene elutes 1.646g. of colorless crystals which are recrystallized from ether-hexane upto constant melting point and clearing point. The pure4'-cyano-4-biphenylyl n-nonyl carbonate obtained melts at 53.0°-53.1°and has a clearing point of 70.0°. The compound is smectic up to 68.1°.UV (EtOH): ε₂₇₁ = 26,600.

EXAMPLE 14 Preparation of 4'-cyano-4-biphenylyl n-decyl carbonate

0.384 G. of 4'-cyano-4-hydroxy-biphenyl are dissolved in 3.2 ml. ofabsolute pyridine and reacted with 0.527 g. of chloroformic acid n-decylester as in Example 1. The 0.822 g. of brownish crystals obtainedaccording to the procedure described in Example 1 are dissolved inbenzene and chromatographed on 40 g. of silica gel. Benzene elutes 0.714g. of colorless crystals which are recrystallized from ether-hexane upto constant melting point and clearing point. The pure4'-cyano-4-biphenylyl n-decyl carbonate obtained melts at 59.3°-60.0°and has a clearing point of 74.0°. The compound is smectic in the entireliquid crystalline range. UV (EtOH): ε₂₇₀ = 26,400.

EXAMPLE 15 Preparation of p-[N-(p-cyanophenyl)formimidoyl]phenyl methylcarbonate

A mixture of 6.1 g. of p-formylphenylcarbonic acid methyl ester and 4.0g. of p-aminobenzonitrile is gassed with argon in 100 ml. of benzene andheated under reflux for 1 hour (bath temperature 135°). The resultingwater is separated with a water separator. During an additional hour,the benzene condensed in the reflux condenser is led back into thereaction vessel through a layer of 100 g. of aluminium oxide (act. I).After cooling, the mixture is freed from solvent in vacuum at 50° bathtemperature, whereby there remain 9.3 g. of practically colorlesscrystals which are recrystallized several times from isopropanol up toconstant melting point and clearing point and up to the disappearance ofside-products in the gas chromatogram. The pure colorlessp-[N-(p-cyanophenyl)-formimidoyl]phenyl methyl carbonate obtained has amelting point of 139.0°-139.2° and a clearing point of 156.0°. UV(EtOH): ε₂₇₄ = 24,100 (shoulders at 315 and 234 nm; minimum at 242 nm).

EXAMPLE 16 Preparation of p-[(p-cyanobenzyliden)amino]phenyl methylcarbonate

A mixture of 0.835 g. of p-methoxycarbonyloxyaniline and 0.655 g. ofp-cyanobenzaldehyde is gassed with argon in 50 ml. of benzene and heatedunder reflux for 1 hour (bath temperature 130°). The resulting water isseparated with a water separator. During an additional hour, benzenecondensed in the reflux condenser is now passed back into the reactionvessel through a layer of 20 g. of aluminium oxide (act. I). Aftercooling, the reaction mixture is freed from solvent in vacuum at 50°C.bath temperature, whereby there remain 1.395 g. of yellowish crystalswhich are recrystallized several times from isopropanol up to constantmelting point and clearing point and up to the disappearance ofside-products in the gas chromatogram. The pure, slightly yellowishp-[(p-cyanobenzyliden)amino]phenyl methyl carbonate obtained has amelting point of 145.1°-146.2° and a clearing point of 163.4°. UV(EtOH): ε₂₇₀ = 20,250, ε₃₂₄ = 10,800 (shoulders at 243 and 221 nm;minima at 312 and 233 nm).

EXAMPLE 17 Preparation of p-[(p-cyanophenoxy)carbonyl]phenyl ethylcarbonate

5.66 G. of p-cyanophenol are dissolved in 66 ml. of absolute pyridineand cooled to -10° with stirring. A total of 8.6 g. of crudep-carbethoxy-oxybenzoyl chloride is then added portionwise thereto overa period of 10 minutes. The temperature rises to 0° and pyridinehydrochloride precipitates out. The mixture is stirred overnight at roomtemperature and the suspension poured on to a mixture of 200 ml. of iceand 200 ml. of 20% hydrochloric acid. Thereafter, this mixture isextracted three times with ethyl acetate, washed with water, dried oversodium sulfate and evaporated under vacuum. The 12.4 g. of reddishcrystals obtained as the residue are dissolved in benzene andchromatographed on 400 g. of silica gel. Benzene-1% acetone (v/v) elute8.1 g. of yellowish crystals which are recrystallized fromacetone-hexane up to constant melting point and clearing point. The purep-[(p-cyanophenoxy)carbonyl]phenyl ethyl carbonate obtained melts at144.7°-144.8° and is liquid crystalline (monotrope) upon cooling to115.8°. UV (EtOH): ε₂₄₁ = 29,700.

The starting material is prepared as follows:

Chloroformic acid ethyl ester is allowed to act on p-hydroxybenzoic acidin the presence of N-caustic soda according to the method of E. Fischer,Ber. 41, 2877 (1908), whereby there is obtained crystallinep-carbethoxy-oxybenzoic acid which is treated with thionyl chlorideaccording to the data of H. Schonenberger et al. Arzneimittelforschung14, 324 (1964). After removal of the excess thionyl chloride in vacuum,there is obtained crude p-carbethoxy-oxybenzoyl chloride which is thenreacted directly as described above.

We claim:
 1. A compound of the formula ##SPC11##wherein R isstraight-chain alkyl of 3 to 8 carbon atoms or straight-chain alkoxy of3 to 10 carbon atoms.
 2. A compound in accordance with claim 1, whereinR is n-butyl, n-pentyl, n-hexyl, n-pentyloxy, n-heptyloxy or n-octyloxy.3. The compound in accordance with claim 1, 4'-cyano-4-biphenylylbutyrate.
 4. The compound in accordance with claim 1,4'-cyano-4-biphenylyl valerate.
 5. The compound in accordance with claim1, 4'-cyano-4-biphenylyl hexanoate.
 6. The compound in accordance withclaim 1, 4'-cyano-4-biphenylyl octanoate.
 7. The compound in accordancewith claim 1, 4'-cyano-4-biphenylyl nonanoate.
 8. The compound inaccordance with claim 1, 4'-cyano-4-biphenylyl n-propyl carbonate. 9.The compound in accordance with claim 1, 4'-cyano-4-biphenylyl n-butylcarbonate.
 10. The compound in accordance with claim 1,4'-cyano-4-biphenylyl n-pentyl carbonate.
 11. The compound in accordancewith claim 1, 4'-cyano-4-biphenylyl n-hexyl carbonate.
 12. The compoundin accordance with claim 1, 4'-cyano-4-biphenylyl n-heptyl carbonate.13. The compound in accordance with claim 1, 4'-cyano-4-biphenylyln-octyl carbonate.
 14. The compound in accordance with claim 1,4'-cyano-4-biphenylyl n-nonyl carbonate.
 15. The compound in accordancewith claim 1, 4'-cyano-4-biphenylyl n-decyl carbonate
 16. The compoundin accordance with claim 1, 4'-cyano-4-biphenylyl heptanoate.